Create method with known identifier then alias into place.

This means we never have to rely on define_method (which is slower and
uses more memory), even when we have attributes containing characters
that are not allowed in standard method names.

(I am mainly changing this because the duplication annoys me, though.)

activerecord/lib/active_record/attribute_methods/read.rb

@@ -42,38 +42,34 @@ def undefine_attribute_methods
         end
 
         protected
-          # Where possible, generate the method by evalling a string, as this will result in
-          # faster accesses because it avoids the block eval and then string eval incurred
-          # by the second branch.
+          # We want to generate the methods via module_eval rather than define_method,
+          # because define_method is slower on dispatch and uses more memory (because it
+          # creates a closure).
           #
-          # The second, slower, branch is necessary to support instances where the database
-          # returns columns with extra stuff in (like 'my_column(omg)').
+          # But sometimes the database might return columns with characters that are not
+          # allowed in normal method names (like 'my_column(omg)'. So to work around this
+          # we first define with the __temp__ identifier, and then use alias method to
+          # rename it to what we want.
           def define_method_attribute(attr_name)
             cast_code = attribute_cast_code(attr_name)
             internal  = internal_attribute_access_code(attr_name, cast_code)
             external  = external_attribute_access_code(attr_name, cast_code)
 
-            if attr_name =~ ActiveModel::AttributeMethods::NAME_COMPILABLE_REGEXP
-              generated_attribute_methods.module_eval <<-STR, __FILE__, __LINE__
-                def #{attr_name}
-                  #{internal}
-                end
-
-                def self.attribute_#{attr_name}(v, attributes, attributes_cache, attr_name)
-                  #{external}
-                end
-              STR
-            else
-              generated_attribute_methods.module_eval do
-                define_method(attr_name) do
-                  eval(internal)
-                end
-
-                singleton_class.send(:define_method, "attribute_#{attr_name}") do |v, attributes, attributes_cache, attr_name|
-                  eval(external)
-                end
+            generated_attribute_methods.module_eval <<-STR, __FILE__, __LINE__
+              def __temp__
+                #{internal}
               end
-            end
+              alias_method '#{attr_name}', :__temp__
+              undef_method :__temp__
+            STR
+
+            generated_attribute_methods.singleton_class.module_eval <<-STR, __FILE__, __LINE__
+              def __temp__(v, attributes, attributes_cache, attr_name)
+                #{external}
+              end
+              alias_method 'attribute_#{attr_name}', :__temp__
+              undef_method :__temp__
+            STR
           end
 
         private

activerecord/test/cases/base_test.rb

@@ -570,10 +570,12 @@ def test_non_valid_identifier_column_name
     weird = Weird.create('a$b' => 'value')
     weird.reload
     assert_equal 'value', weird.send('a$b')
+    assert_equal 'value', weird.read_attribute('a$b')
 
     weird.update_column('a$b', 'value2')
     weird.reload
     assert_equal 'value2', weird.send('a$b')
+    assert_equal 'value2', weird.read_attribute('a$b')
   end
 
   def test_multiparameter_attributes_on_date